Lactic acid bacteria play an important role in maintaining the balance of normal gastro-intestinal microflora. Diet, stress, microbial infection and intestinal diseases disturb the microbial balance, which often leads to a decrease in the number of viable lactic acid bacteria (especially lactobacilli and bifidobacteria) in the intestinal tract. The subsequent uncontrolled proliferation of pathogenic bacteria then leads to diarrhoea and other clinical disorders such as cancer, inflammatory disease and ulcerative colitis.
One of the key properties of probiotic lactic acid bacteria is the adhesion of cells to epithelial cells or intestinal mucus. This requires strong interaction between receptor molecules on epithelial cells and bacterial surfaces. Adhesion of probiotic cells prevent the adhesion of pathogens and stimulate the immune system. The latter is achieved by interacting with mucosal membranes, which in turn sensitises the lymphoids. Another important characteristic of probiotics is survival at low pH and high bile salts.
Certain strains of bifidobacteria, lactobacilli and enterococci associated with the intestines of humans and animals are known to produce bacteriocins (antimicrobial peptides). The role of these peptides, and their significance in controlling the proliferation of pathogenic bacteria in the intestinal tract, is uncertain. However, as concluded from recent reports on bacteriocins active against Gram-negative bacteria, there may be renewed interest in these peptides and their interaction with intestinal pathogens. Many of the latter bacteriocins are produced by lactic acid bacteria normally present in the intestinal tract, viz. the Lactobacillus acidophilus-group, Lactobacillus reuteri, Lactobacillus casei, Lactobacillus fermentum, Lactobacillus plantarum, Lactobacillus pentosus, Lactobacillus paracasei subsp. paracasei and Enterococcus faecalis. 
The invention describes a strain of Enterococcus mundtii that resists intestinal stress conditions (e.g. low pH, bile salts, salts, pancreatic enzymes) and produces a broad-spectrum antibacterial peptide (peptide ST4SA).